WINTER-WHEAT SEEDLING EMERGENCE FROM DEEP SOWING DEPTHS

Growers in low-precipitation (<300 mm annual) dryland wheat-fallow are as of the inland Pacific Northwest need winter wheat (Triticum aestivu m L.) cultivars that emerge from deep sowing depths in dry soils. Stan d establishment is the most important factor affecting winter wheat gr ain yield in this region. Despite poor resistance to disease, modest g rain yield potential, and otter problems, the outdated soft white wint er wheat (SWWW) cultivar Moro is widely sown in these dry areas, due t o its excellent emergence ability, All other SWWW cultivars are semidw arfs that carry emergence-impeding Rht(1) or Rht(2) reduced-height gen es, From 12 solving trials at 2 locations over 4 yr, we compared the e mergence capability of Moro to (i) 8 SWWW cultivars and (ii) 16 SWWW a dvanced experimental Moro-replacement lines. Under both wet and dry so il conditions (soil water content in the seed zone ranged from 11 to 1 9 mm(2) mm(-3)), seeds were sown deep, with 110 to 160 mm of soil cove r. Moro always emerged fastest and achieved the best final stand compa red with the semidwarf cultivars, The advanced experimental lines, whi ch contained either no reduced-height gene or a Rht(1), Rht(2), or Rht (8) reduced-height gene, had superior straw strength, disease resistan ce, and grain quality compared with Moro, The best-emerging advanced e xperimental lines had coleoptile lengths >100 mm, Coleoptile length wa s associated with emergence capability among both cultivars (r(2) = 0. 71, P < 0.004) and advanced lines (r(2) = 0.62, P < 0.001), From deep sowing depths in this study: (i) cultivars and advanced lines with Rht (1) and Rht(2) reduced-height genes always emerged poorly compared wit h Moro: (ii) the Rht(8) reduced-height gene did not hamper emergence t o the extent that Rht(1) and Rht(2) did; and (iii) several advanced ex perimental lines with long coleoptiles equaled or exceeded Moro for em ergence.